This turned out to be two long heavyweight movements with a short lightweight little Canto in between. Founded on a 9 note mode (similar to Messiaen's 3rd mode, but not used in the same way and not always adhered to), each of the three movements is in ABA form, with the reprise shorter. The 1st movement explores durations at several levels; the 3rd explores transposition, inversion, variation, decoration and pattern exchange. Not as hard nosed as that may seem!